Various woods comprise relatively high levels of extractives that include, for example, oils, rosin and tannin, which can migrate to the surface of the wood. While this migration will often happen over time, it can also be accelerated upon application of heat. Accordingly, this migration can be particularly problematic when a UV curable coating is applied to the wood; the heat from the UV lamps can cause extractives to migrate to the surface and interfere or retard the UV cure of the coating. This migration can also lead to adhesion problems between the coating and the wood. These adhesion problems can be observed both at the time of coating and also subsequently, when “lifting” of the coating may be observed. In addition to the adhesion issues that this migration causes, it can also cause subsequent staining or discoloration of the coating.
Currently available primers for these types of woods, including two component solvent-based urethanes and compositions having tannin blocking components, are only moderately successful in impeding the migration of extractives to the surface of the wood. Accordingly, improved primers for high extractive content wood are desired. Waterborne coatings are particularly desirable for handling, environmental and other reasons.